In general, to control an in-door robot moving indoors, it is required to recognize a position of the robot. Generally, there are two self-position calculation methods performed by a robot itself using a camera.
First, there is a method of using an artificial landmark. As shown in FIG. 1, a landmark 30 having a certain meaning is installed on a ceiling or a wall, the landmark 30 is photographed by a camera 20, the landmark 30 is extracted from an image, and coordinates on a screen are allowed to be identical with coordinates of a mobile robot 10, thereby calculating a self-position of the mobile robot 10 by itself (refer to Korean Patent No. 485696).
On the other hand, as shown in FIG. 2, the landmark 30 may be installed on a top of the mobile robot 10 and the camera 20 may be installed on the ceiling.
Second, there is a method of using a natural landmark. A ceiling is photographed by a camera, information of structures such as lightings installed on the ceiling and straight lines and edges of interfaces between the ceiling and walls is extracted, thereby calculating a self-position of a mobile robot by itself using the information (refer to Korean Patent No. 483566).
However, when using the artificial landmark, the artificial landmark may be affected by lightings and color information of the landmark may be distorted by sunlight. Also, when using the natural landmark, since the natural landmark is much affected by brightness of an ambient light and there is required odometer information or another robot position reader when recording a position of a feature of in the landmark, a large memory is required and an additional device is essential. Particularly, when there is no illumination, it is very difficult to use the natural landmark.
Accordingly, it is required a new self-position recognition method of a mobile robot, capable of being not affected by lightings and reducing a calculation of the image pre-processing.
Also, when using the two conventional methods described above, since coordinates of a camera and coordinates of a landmark attached to a ceiling calculate position information of a mobile robot while assuming that there is no rotation of in directions excluding the direction of gravity, the robot position information calculated using an image obtained by the camera may have many errors when the mobile robot goes over a small mound or is inclined by an external force or an inertial force of rapid acceleration or deceleration.
On the other hand, though there may be an initial correction for an inclination occurring when attaching one of a CMOS and CCD sensors used for a camera device to a robot, the initial correction is merely for an error occurring when initially installing but not for an error caused by an inclination occurring while the robot is actually driving.